A plant line can be called vigorous when this line grows vitally, healthy, is tolerant to various biotic and abiotic stresses and most importantly has a high yield.
The currently used method to classify plant lines according to their growth and yield vigour consists in performing field trials at different locations. A disadvantage of field trials is that, at best, only two experiments can be done each year. Even when field trials are planned very well and deliver the appropriate data, this time constraint interferes with the continuity of the projects and slows down the progress.
A number of assays (mainly qualitative) have been described for use in plant tissue culture to study the effect of various stresses on the survival of cells or tissues (Towill and Mazur, 1975; Chen et al. 1982, Duncan and Widholm 1990, Stepan-Sarkissian and Grey, 1990; Upadhyaya and Caldwell, 1993; Enikeev et al., 1995; Ishikawa et al., 1995; Popov and Vysotskaya, 1996). These are actually “viability” assays which do not measure the fitness or vigour of the cultures.
Chlorophyll fluorescence and fluorescence imaging may also be used to study the influences of stress conditions on whole plants (Lichtenthaler, 1996; Lichtentaler and Mieké, 1997). Although these assays provide some data on the tolerance of the plant lines to certain stresses, they cannot be used to measure growth and yield vigour.
Published PCT application “WO” 97/06267 and U.S. Pat. No. 6,074,876 (incorporated herein by reference) describe the use of PARP inhibitors to improve the transformation (qualitatively or quantitatively) of eukaryotic cells, particularly plant cells. Also described is a method for assessing the agronomical fitness of plants or plant material by measuring the electron flow in the mitochondrial electron transport chain.
None of the prior art documents describe an in vitro method allowing to predict the combining ability of parent inbred plant lines, nor do they describe an in vitro method allowing to determine good combinations of parent inbred plant lines capable of yielding hybrid lines with high heterosis. Such in vitro physiological methods would represent an extra tool to rapidly identify parental and hybrid lines of interest in breeding programs and could result in a significant gain of time.
The current invention provides such methods as described in the various embodiments and claims disclosed herein.